Like whitecaps on the surf, thousands of homemade signs bobbed above the sea of protesters who surged through downtown streets in last weekend’s women’s march against President Trump in Los Angeles.

The messages were blunt (“Trump is a racist”), earnest (“Kindness is everything”), witty (“Bad Hombre Raised by Nasty Woman”), and punctuated by variations on the theme that even the Secret Service couldn’t protect the new president if he tried to grab the sign-holder the way he described in his Access Hollywood video.

But the most politically relevant message may have been written on a hand-lettered, four-word sign that inverted a famous catchphrase from Star Trek. “Resistance Is Not Futile,” it read.

It’s easy to understand why Democrats would feel otherwise. In last November’s election, Hillary Clinton won more than 65.8 million votes. That was more than any candidate in American history except Barack Obama in 2008 and 2012 (and he just barely beat her haul the second time). Clinton beat Trump in the popular vote by nearly 2.9 million votes. With that she marked the sixth time in the past seven presidential elections that Democrats have won the popular vote—a record unmatched since the formation of the modern party system in 1828.

And yet, Democrats emerged from Trump’s inaugural completely excluded from federal power, with Republicans simultaneously controlling the White House, House, and Senate. In state governments, Democrats began the Trump era at a low ebb, too.

So for many of those I spoke with, the march’s first purpose was to find reassurance that they were not isolated in their undiminished opposition to Trump. “More than anything we want to feel that we’re not alone,” said Mina Olivera from West Los Angeles, who marched with her husband and two children. “We just cannot be quiet and let it happen.”

Olivera’s simple declaration captured what is likely to be the march’s most important political impact. The unprecedented turnout—which by the best estimates drew about one in every 100 Americans into the streets—sent the message that even after Trump’s upset victory there is a still a huge mass of Americans viscerally opposed to him. “We’re trying to show we have a voice and we’re not scared,” Roger Palencia, a marcher from Whittier, California, told me.

For many marchers, that message’s principal audience wasn’t Trump, or even congressional Republicans. Instead, the target was congressional Democrats, who protesters expected to do whatever they could “to hold the line” against Trump, as Erica Mayorga of Whittier put it.

That sentiment is where a comparison to the Tea Party movement may be most aptly applied. The Tea Party eruption in summer 2009 had no discernible impact on then-President Obama’s decisions, and relatively little on congressional Democrats’ either. But the uprising sharpened congressional Republicans’ resistance to Obama. The effect was particularly evident on health-care reform, when the Tea Party’s emergence doomed Obama’s hopes of reaching a bipartisan Senate agreement.

It’s true, as skeptics have noted, that even if the women’s marches inspire sustained activism, that wouldn’t answer the key long-term challenges Democrats face. Based predominantly, though not exclusively, in urban areas, the marches reflected the excessive concentration of Democratic support in big cities and coastal states—a concentration that largely explains why the party holds so little power despite consistently amassing a bigger national coalition than the GOP since the 1990s.

But movements usually matter more in generating opposition than in formulating alternatives; they typically function more as a red light than green. It’s difficult, for instance, to see Trump’s rise as a policy victory for the Tea Party movement. Trump’s agenda on several fronts, like infrastructure and health-care spending, could even revive the “big-government conservatism” of George W. Bush that infuriated Tea Partiers. Still, by creating demand for a more militant party, the movement reconfigured the GOP and helped pave Trump’s bellicose run to its nomination.

If it becomes a sustained movement, the women’s march might similarly reorient Democrats. Democratic elected officials remain divided over the right balance between confronting and cooperating with Trump. Privately, some leading Democratic strategists worry that Senate Minority Leader Chuck Schumer, despite some forceful criticism, will lean too much toward making deals with Trump, rather than working to systematically mobilize resistance and limit his support—as Senate Republicans, under Tea Party pressure, did against Obama.

Some deal-making may be unavoidable since Schumer must worry about protecting 10 Democratic senators facing 2018 reelection races in states Trump carried. But Saturday’s marches—like the Tea Party uprising—signaled that the passion in the party tilts decidedly toward resistance. Post-inaugural polls reinforce that conclusion. In the Gallup Poll this week, Trump became the first newly inaugurated president to enter office with a positive job rating from less than half of Americans. And just 14 percent of Democrats said they approved of his performance, while 81 percent disapproved. That was by far the lowest initial approval rating for a new president from voters in the opposite party. Bush, at 32 percent, marked the previous low.

Trump’s tumultuous first week made clear that even after his narrow victory he is determined to pursue the sweeping policy changes, at home and abroad, that typically follow a landslide. The massive crowds that braved winter weather in most places to march last weekend testified to how many Americans are equally determined to resist him at every step. “It’s the liberal side of the Tea Party,” said Joyce Holiday of Granada Hills, as the Los Angeles crowd swirled around her. “We’re going to fight.” The lines are quickly hardening in a presidency that may divide America like no other.

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